I can remember noticing this a few months back already, but never thought much of it back then. I initially thought it might have been intentional, because people were so happy to finally have another grass variation when the Africa DLC/update came out. But I haven't really used the drin grass since then, because there was this weird flickering bug with the grass that made it really uncomfortable to look at. That seems to have been fixed now though.
I just tried to fill my entire Okapi habitat with the grass, covering every square inch. Still, the plants coverage in the welfare tab only registers as 43% due to some of the trees I have there, and the grass is also not listed in the plants section for the animal. So, since it's such a generic item, I assume it might have been changed to ensure that it can be used anywhere! Wondering if that was mentioned in any patch notes, because I hope they will not change that back again.